Tokkai No. 2000-234509 published by the Japanese Patent Office in 2000 discloses an exhaust gas purification device which carries out the purification of particulate matter discharged from a diesel engine or the like. The purification device comprises a filter in the engine exhaust system, the filter being regenerated by oxidizing or incinerating the trapped particulate matter at a predetermined interval.
In addition to combustible particulate matter, non-combustibles (hereafter, referred to as “ash”) mainly from engine oil additives also adhere to the filter. As the ash cannot be burnt in the process of regeneration, after a certain time interval has elapsed, it will cause a pressure loss in the filter, and a reduction of active filter surface area. For this reason, the filter needs maintenance such as replacement or washing according to use.